All engines—diesel, gasoline, propane and natural gas—produce exhaust gas containing carbon monoxide, hydrocarbons, and nitrogen oxides (“NOx”). These emissions are the result of incomplete combustion. Additionally, diesel engines also produce particulate matter (“PM”). As more focus is placed on health and environmental issues, governmental agencies throughout the world are enacting more stringent emissions laws.
Because so many diesel engines are used in trucks, the U.S. Environmental Protection Agency and its counterparts in Europe and Japan first focused on setting emissions regulations for the on-road market. While the worldwide regulation of nonroad diesel engines came later, the pace of cleanup and rate of improvement has been more aggressive for nonroad engines relative to on-road engines.
Manufacturer of nonroad diesel engines are expected to meet specific emissions regulations. For example, Tier 3/Stage III A emissions regulations required an approximate 65 percent reduction in PM and a 60 percent reduction in NOx from 1996 levels. As a further example, Interim tier 4/Stage III B regulations required a 90 percent reduction in PM along with a 50 percent drop in NOx. Still further, Final Tier 4/Stage IV regulations which will be fully implemented by 2015, will take PM and NOx emissions to near-zero levels.
PM is a non-gaseous product of combustion commonly seen as smoke. It is made up of carbon, which is incompletely burned fuel and hydrocarbons, and is the visible, black smoke. PM also contains sulfuric acid which is created from the sulfur found in diesel fuel. PM and ash may both be trapped in, for example, a diesel particulate filter (“DPF”).
To reduce the remaining NOx, a power system may comprise an exhaust gas recirculation (“EGR”) system. The EGR system recirculates a portion of the engine's exhaust gas back into an intake manifold of the engine. The recirculated portion of the exhaust gas reduces the concentration of oxygen therein, thus lowering the combustion temperature, slowing the chemical reactions, and decreasing the formation of NOx. However, because the recirculated portion of the exhaust as may contain water vapor—the amount of water vapor being dependent on the humidity of the air and the fuel quantity burned—excessive cooling may result in condensation in the EGR system.
One problem associated with condensation, in the recirculated portion of the exhaust gas, is that it may not uniformly flow into the engine's cylinders. This may result in excess NOx in some cylinders and simultaneously excess PM in other cylinders. Another problem is that under some other operating conditions, there may be so much condensation that it may form pools and rivers. Such conditions may lead to poor ignition characteristics. What is needed, in the art, is a condensation injection system that addresses these issues.